Flu vaccine less effective against mutant strain

Dr. Danuta Skowronski is an epidemiologist with the B.C. Centre For Disease Control.

This year’s flu shot may prove less effective than usual because the dominant virus now circulating has mutated significantly in the months since the vaccine was devised.

The H3N2 strain – one of three targeted in this year’s flu vaccine – is thought to have changed its genetic makeup enough to possibly thwart the antibodies that the vaccine activates.

Dr. Danuta Skowronski, an epidemiologist with the B.C. Centre for Disease Control, is still recommending the vaccine, particularly for the elderly, the chronically ill and those with compromised immune systems.

“It’s not a perfect match,” she said. “But for the high risk, even an imperfectly matched vaccine is going to give cross protection. And for some people it could be life-saving.”

She said the H3N2 strain tends to be particularly nasty to the elderly and may bring a deadlier flu season than usual.

“We may see more hospitalizations or deaths this year,” Skowronski said.

She said it’s particularly concerning that the flu has struck B.C. surprisingly early this season, causing outbreaks in eight seniors’ care homes.

The vaccine was formulated last February because it takes six to eight months to produce in large quantities and the H3N2 virus is thought to have since mutated while circulating in the southern hemisphere.

Skowronski said it’s still not too late to get the shot and some protection when flu activity peaks in the weeks ahead, including any later surge of cases of influenza B, which tends to peak in March or April.

The vaccine also targets the influenza B and H1N1 viruses, but they’re considered less likely to cause illness this flu season.

Even in years when the vaccine is a better fit – last year’s was about 70 per cent effective against the then-dominant H1N1 strain – Skowronksi says everyone should wash their hands frequently and avoid touching their eyes, nose and mouth.

People who get the flu shot often mistakenly think any illness they contract can’t be flu and sometimes fail to get appropriate treatment.

“It doesn’t make you invincible,” Skowronski said.

Anti-viral medication can stop or fight an influenza infection but must be given quickly, ideally within 12 hours of the start of symptoms.

An estimated 3,500 Canadians die each year from flu complications – mainly seniors and others with underlying conditions.